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Kepler satellite

This past week's issue of Nature offers tantalizing data to suggest the Earth could survive the sun's expansion when it enters into red giant phase seven billion years from now.

By 'survive' I mean remain in one piece. The paper by Stéphane Charpinet of University of Toulouse in France, reports his team's interpretation of data from the Kepler satellite which reveals two planets inside the orbit of an evolved star listed as KIC 05807616.

By 'evolved', Charpinet means a star that exhausted its hydrogen core long ago, swelled into a red giant, before contracting to a hot B subdwarf.

But KIC 05807616 is also a variable star that brightens and dims at regular intervals.

According to Charpinet's paper, A compact system of small planets around a former red giant star, the astronomers were analyzing data from Kepler, which had been monitoring the star's oscillations, when they discovered further variability at two different times that did not seem to be caused by the star's more rapid intrinsic pulsations.

According to Eliza M. Kempton's report:

The variability that results from these subtle shifts in the planets' reflected and emitted light is tiny. Charpinet et al. found that this variability is present at a level of only several hundredths of one percent, which means that the planets themselves are probably quite small.

Indeed, the planets could be comparable to the Earth's size, in their estimation. And what makes this fascinating is that it adds a twist to an assumption astrophysicists have long held --that any planets within an astronomical unit (the distance between Earth and the sun) during its expansion to red-giant phase, would be completely destroyed. It's certainly been the standard scenario painted for Earth in the far future. Indeed life on Earth, and any atmosphere, will be long gone even before the sun swells into a red giant.

Charpinet's paper suggests that such planets could survive. Either by shifting to a wider orbit as the star expands, or by toughing out the absorption until the star contracts.

It's also possible, the team's paper points out, that the two planets orbiting KIC 05807616 are new planetary bodies formed out of the debris of the previous ones after the star contracted into its subdwarf status.

Nevertheless: "These bodies probably survived deep immersion in the former red-giant envelope," they write. "They may be the dense cores of evaporated giant planets that were transported closer to the star during the engulfment and triggered the mass loss necessary for the formation of the hot B subdwarf, which might also explain how some stars of this type did not form in binary systems."